private void btQuayLai_Click(object sender, EventArgs e)
{
Dang_Nhap dn = new Dang_Nhap();
this.Visible = false;
dn.ShowDialog();
this.Close();
}
private void btQuayLai_Click(object sender, EventArgs e)
{
Form frm = Application.OpenForms["Dang_Nhap"];
if (frm == null)
{
frm = new Dang_Nhap();
}
this.Hide();
frm.Show();
}
